Enzyme histochemistry in muscle and nerve biopsies is carried out for diagnostic purposes in patients with several neuromuscular disorders. Immunocytochemical studies were conducted using specific antibodies to thymic peptides to investigate changes in the distribution of epithelial cells and thymocytes in the thymus of patients with myasthenia gravis. Using the cytofluorograph, specific subsets of lymphocytes that carry thymic markers (thymosin alpha1, alpha7, beta4) were defined. The interaction between cells of the lymphoid and central nervous system was investigated searching for common antigenic markers on their cell surface. Thymosin beta4, an immunomodulating polypeptide, was found to be a common antigen shared by macrophages, dendritic lymphoid cells and oligodendrocytes. The immunoglobulin of certain patients with paraproteinemic polyneuropathies has been identified as a specific antibody to myelin associated glycoprotein; nerve biopsies from these patients are studied by electron microscopy and immunocytochemically with specific antimyelin antibodies. The nature of amyloid protein in 15 patients with "sporadic" amyloid polyneuropathy was identified immunocytochemically using specific antibodies to amyloid proteins; the immunocytochemical findings were confirmed biochemically on the extracted amyloid tissue. Immune cellular markers were investigated during evolution of EAN and EAE induced in rhesus monkeys and therapies were attempted using some novel immunomodulating agents. The mechanism of mouse hepatitis virus-induced demyelination was investigated in mice inoculated with mouse hepatitis virus; the distribution of viral antigens ws demonstrated in the demyelinated regions. Inflammatory myopathy was identified in monkeys with immunodeficiency (Simian AIDS) and antibodies to retrovirus D immunoreacted with the infiltrating inflammatory cells and muscle capillaries.